Electrophotographic processes for producing a permanent image on media are well known and commonly used. In general, these processes all include: (1) charging a photoreceptor which is a drum or continuous belt bearing a photoconductive material; (2) producing an electrostatic latent image by exposing the charged area to a light image or a light emitting diode array, or scanning the charged area with a laser beam; (3) presenting particles of toner to the photoreceptor surface upon which the electrostatic latent image is disposed so that the particles are transferred to the electrostatic latent image; (4) transferring the particles from the photoreceptor to the media while maintaining the shape of the image formed on the photoreceptor drum; (5) fusing or fixing the particles in the shape of the image to the media; and (6) cleaning or restoring the photoreceptor for the next printing cycle.
Referring to FIG. 1, the electrophotographic printer 300 of the prior art has therein feed rollers 321 and 322 for feeding the printing sheets stacked in the printing sheet cassettes 311 and 312, a pair of rollers 323 for conveying a printing sheet fed from the printing sheet cassettes 311 or 312, an exposure array 376 for emitting light to the photosensitive drum 52 for forming an electrostatic latent image on the photosensitive drum 52, a transfer electrostatic charger 327 for transferring toner from the photoconductive drum 52 to the printing sheet, a pair of heat rollers 328 for fixing the toner transferred on the printing sheet and a prior art electrophotographic cartridge 50. The prior art electrophotographic cartridge 50 is not designed for replenishment of the toner supply.
The electrophotographic cartridge 50 has an electrostatic charger 84 for electrostatically charging the photoconductive drum 52 uniformly, a developer assembly 54 for applying toner to the electrostatic latent image formed on the photoconductive drum 52 after exposure to the exposure array 376, and a cleaner 76 for removing the untransferred toner which remains on the photoconductive drum 52 after the transfer step. The untransferred toner is stored in waste hopper 85. Electrostatic charger 84 may be a charge roller assembly or a corona assembly. Further information about alternative photographic processes is available in the text "The Physics and Technology of Xerographic Processes", by Edgar M. Williams, 1984, a Wiley-lnterscience Publication of John Wiley & Sons, the disclosure of which is hereby incorporated by reference.
Many image forming apparatus utilize the electrophotographic printing process, examples being laser printers, copy machines, and facsimile machines. As described above, these image forming apparatus use toner to print or copy the desired image or words onto a piece of paper or media. The toner is contained in a reservoir which is depleted as a result of printing. For example, the toner in a laser printer is generally depleted after printing from 2,000 to 10,000 pages depending upon the initial supply of toner in the reservoir and the coverage of the text or graphics images printed.
Some electrophotographic printing systems, such as copy machines, are designed to allow recharging of the toner reservoir. On these electrophotographic printing systems, an access port to the toner reservoir has been included to allow an operator to recharge the toner reservoir. Typically, toner is supplied in bottles and the operator is required to pour the toner into the toner reservoir to recharge the printing system. This creates the potential for contamination of the recharged toner supply and the potential for spillage of the toner during the recharging process. Contamination of the recharged toner supply can cause a degradation in the print quality delivered by the printing system either directly as a result of the contamination or through interaction with electrophotographic printing components. Spillage of toner and the possible subsequent soiling of hands, clothes, papers, and office equipment results in customer dissatisfaction.
Electrophotographic printers are typically designed so that the components involved in actually accomplishing electrophotographic printing are contained in a disposable electrophotographic print cartridge. The components usually included in the cartridge are the photoconductor drum, the drum charging assembly, such as the charge roller assembly or the corona assembly, the developer assembly, the drum cleaning blade, and the supply of toner used for forming the print text or print images. The supply of toner is contained in a toner reservoir. The useable life of the cartridge is limited by the available supply of toner in the toner reservoir and the useable life of the cartridge components, particularly the photoconductor, the developer assembly, and the drum charging assembly. Practically, limitations on the size and weight of the cartridge, which limit the supply of toner, most significantly limit the useable life of the cartridge. Cartridge components are designed to perform acceptably well for print cycles beyond the number at which the toner is consumed. The organic photoconductor drum, which is in contact with the media during printing, usually is the first of the cartridge components to fail because of wear. Typically, no provision for refilling the toner reservoir of the cartridge is included in the design of the cartridge. Upon exhaustion of the toner supply in the cartridge, it is necessary to replace the empty cartridge with one having the reservoir filled with toner.
An electrophotographic printer which allows recharging of the toner reservoir easily and with a greatly reduced risk of spillage would provide the motivation for the development of electrophotographic components with an extended operating life to exploit the refilling capability. Because electrophotographic cartridges are relatively expensive, this would allow a significant reduction in the average cost per printed page resulting from the extended operating life.
Disposal of exhausted electrophotographic cartridges contributes to the consumption of available landfill space. An additional benefit of cartridge toner recharging capability would be a reduction in the volume of solid waste generated through the use of electrophotographic cartridges.